.TH cpudist 8  "2016-06-28" "USER COMMANDS"
.SH NAME
cpudist \- On- and off-CPU task time as a histogram.
.SH SYNOPSIS
.B cpudist [\-h] [-O] [\-T] [\-m] [\-P] [\-L] [\-p PID] [interval] [count]
.SH DESCRIPTION
This measures the time a task spends on the CPU before being descheduled, and
shows the times as a histogram. Tasks that spend a very short time on the CPU
can be indicative of excessive context-switches and poor workload distribution,
and possibly point to a shared source of contention that keeps tasks switching
in and out as it becomes available (such as a mutex).

Similarly, the tool can also measure the time a task spends off-CPU before it
is scheduled again. This can be helpful in identifying long blocking and I/O
operations, or alternatively very short descheduling times due to short-lived
locks or timers.

This tool uses in-kernel eBPF maps for storing timestamps and the histogram,
for efficiency. Despite this, the overhead of this tool may become significant
for some workloads: see the OVERHEAD section.

Since this uses BPF, only the root user can use this tool.
.SH REQUIREMENTS
CONFIG_BPF and bcc.
.SH OPTIONS
.TP
\-h
Print usage message.
.TP
\-O
Measure off-CPU time instead of on-CPU time.
.TP
\-T
Include timestamps on output.
.TP
\-m
Output histogram in milliseconds.
.TP
\-P
Print a histogram for each PID (tgid from the kernel's perspective).
.TP
\-L
Print a histogram for each TID (pid from the kernel's perspective).
.TP
\-p PID
Only show this PID (filtered in kernel for efficiency).
.TP
interval
Output interval, in seconds.
.TP
count
Number of outputs.
.SH EXAMPLES
.TP
Summarize task on-CPU time as a histogram:
#
.B cpudist
.TP
Summarize task off-CPU time as a histogram:
#
.B cpudist -O
.TP
Print 1 second summaries, 10 times:
#
.B cpudist 1 10
.TP
Print 1 second summaries, using milliseconds as units for the histogram, and include timestamps on output:
#
.B cpudist \-mT 1
.TP
Trace PID 186 only, 1 second summaries:
#
.B cpudist -P 185 1
.SH FIELDS
.TP
usecs
Microsecond range
.TP
msecs
Millisecond range
.TP
count
How many times a task event fell into this range
.TP
distribution
An ASCII bar chart to visualize the distribution (count column)
.SH OVERHEAD
This traces scheduler tracepoints, which can become very frequent. While eBPF
has very low overhead, and this tool uses in-kernel maps for efficiency, the
frequency of scheduler events for some workloads may be high enough that the
overhead of this tool becomes significant. Measure in a lab environment
to quantify the overhead before use.
.SH SOURCE
This is from bcc.
.IP
https://github.com/iovisor/bcc
.PP
Also look in the bcc distribution for a companion _example.txt file containing
example usage, output, and commentary for this tool.
.SH OS
Linux
.SH STABILITY
Unstable - in development.
.SH AUTHOR
Sasha Goldshtein
.SH SEE ALSO
pidstat(1), runqlat(8)
